Phenyl N-tert-butyl nitrone (PBN) is a spin trap and a free radical scavenger. PBN has been shown to have a variety of pharmacological effects, such as preventing death after endotoxin-induced shock in rodents and increasing the average life span of senescence-accelerated mice. PBN's radical-trapping capabilities are suggested to be responsible for these effects; however, no hard evidence has been obtained for this assumption. In our preliminary studies, using a new method of nitric oxide (NO) detection, PBN was found to inhibit induction of NO synthase (NOS) in vivo in a mouse endotoxin shock model, as well as in activated macrophages in vitro, suggesting that PBN's protective activity could be explained by suppression of overproduction of NO through inhibition of NOS induction. Preliminary data indicate that some PBN-type nitrone spin traps are more effective than PBN itself in the inhibition of NOS induction. Therefore, many PBN-type spin traps will be tested to elucidate structural dependence of the inhibition capacity. Compelling evidence indicates that NOS expression is modulated by oxidant-sensitive transcription factor, nuclear factor kB (NFkB). Therefore, the hypothesis that radical scavenging by PBN-type spin traps decreases the intracellular concentrations of free radicals, thereby preventing NFkB activation and subsequent induction of iNOS, will be tested experimentally. The specific aims of this project are (A) to determine the structural factors of PBN-type spin traps required for effective inhibition of iNOS induction, (B) to determine the correlation between radical-trapping efficiency of PBN spin traps and the expression of an oxidant-responsive transcription factor, NFkB. The long-term goal of these studies is development of improved drugs for treatment of septic shock and other diseases caused by NO overproduction in human patients.